Hello, I am new to the forum and wonder if anyone can give me any insight on a drone type noise my truck exhibits between 1700-1800 rpm.


Truck is completly stock and made this noise since new. Drone is the only way I know how to describe it. Althought it does not seem to be exhaust in nature. I can faintly "feel" it in the steering wheel and floorboard. It is not speed specific it is rpm specific. Always at 1700-1800 rpm in any gear. If I stay at this rpm it is constant if I accelerate above or slow to below this rpm it goes away.


Engine or transmission harmonics?


Any insight would be greatly appreciated. Other than this minor annoyance I love the truck.Edited by: blackmax04

I've noticed mine does that between 60 and 65 mph. Drone or hum is a good description. I have not checked rpm as it always happens at pretty much the same speed. For me its probably closer to 2000 rpm. For mee it seems to be more spped specific. Mine is a 2005.

I have been told that GM calls this a "boom" and it is harmonics. Mine is speed related it starts at ~56 mph and continues to ~59 mph. If I hold my speed in that range the sound continues. Above or below just the mellow sound of the Dmax producing HP and torque.http://www.dieselplace.com/forum/smileys/Cool.gif My truck makes the same noise on deceleration through my "boom" zone.

Thanks for the replies so far.


oozamalak-that is the mph range that mine is in top gear at the rpm's I stated but, mine does it in all gears at 1700-1800.


Does anyone know the underlying cause of this "boom" or harmonics?


Thanks again for any and all replies.

blackmax04,


I checked on the way home last night and mine does exactly the same thing. At 1800rpm between 58 and 59 miles per hour. Seems more speed related. It drops off quickly before or after these speeds with little variation in the rpm so I'm not sure if its rpm related.


I haven't checked yet to see if it does it at that rpm at other speeds but that is the only place I have noticed it so far. At 58 - 59 on the highway I'm pretty much always at about 1800 rpm.


I have noticed that I do get some noise that is very similar at shift points.

Will it make the drone if you are sitting still and just rev the engine to the required rpm?

Haven't tried it but I will and let you know what happens...

The definition for harmonic is a wave whose frequency is a whole-number multiple of that of another. A harmonic is created when the length of the sound wave is an equal number of devisions or multiples of the length of the item vibrating or moving. For example, if you hit something and it rings and you hear 2 different pitches, one is a harmonic of the other. Something in the driveline or exhaust likes 1800 rmp and it makes it "sing" or drone if you prefer because of it being a lower pitch. http://www.dieselplace.com/forum/smileys/Geek.gif

Checked it out while driving around at lunch today. It is RPM, not speed related. Seems to be right around 1800 rpm. I hear it at the shift points because 1800 is right around where it usually shifts. I hear it at 65 because usually on the highway its turning around 1800 at 65.


Tried reving it to 1800 while in neutral and did not really hear it.

Sorry, I've been out of town guys.


I also tried reving mine in neutral and did not hear it at all. I was just curious if any one else had heared the same thing with their lly. A friend of mine has 2 LB7 D/A's and neither of his make the noise. So I didn't know if it was a characteristic of the LLY or if it was something I needed to be concerned with.


Hoping some of the diesel techs might give some insight.


Thanks again everyone.